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      </div>
    
  </div>


  
  <h1 id="第七章-C控制语句：分支和跳转"><a href="#第七章-C控制语句：分支和跳转" class="headerlink" title="第七章 C控制语句：分支和跳转"></a>第七章 C控制语句：分支和跳转</h1><h2 id="7-1-if语句"><a href="#7-1-if语句" class="headerlink" title="7.1 if语句"></a><a href="#7.1">7.1 if语句</a></h2><h2 id="7-2-if-else语句"><a href="#7-2-if-else语句" class="headerlink" title="7.2 if else语句"></a><a href="#7.2">7.2 if else语句</a></h2><h3 id="7-2-1-介绍getchar"><a href="#7-2-1-介绍getchar" class="headerlink" title="7.2.1 介绍getchar()"></a>7.2.1 介绍getchar()</h3><h3 id="7-2-2-ctype-h-系列的字符函数"><a href="#7-2-2-ctype-h-系列的字符函数" class="headerlink" title="7.2.2 ctype.h 系列的字符函数"></a>7.2.2 ctype.h 系列的字符函数</h3><h3 id="7-2-3-多重选择else-if"><a href="#7-2-3-多重选择else-if" class="headerlink" title="7.2.3 多重选择else if"></a>7.2.3 多重选择else if</h3><h3 id="7-2-4-else与if配对"><a href="#7-2-4-else与if配对" class="headerlink" title="7.2.4  else与if配对"></a>7.2.4  else与if配对</h3><h3 id="7-2-5-多层嵌套的if语句"><a href="#7-2-5-多层嵌套的if语句" class="headerlink" title="7.2.5 多层嵌套的if语句"></a>7.2.5 多层嵌套的if语句</h3><h2 id="7-3-逻辑运算符"><a href="#7-3-逻辑运算符" class="headerlink" title="7.3 逻辑运算符"></a><a href="#7.3">7.3 逻辑运算符</a></h2><h3 id="7-3-1-备选拼写：iso646-h-头文件"><a href="#7-3-1-备选拼写：iso646-h-头文件" class="headerlink" title="7.3.1 备选拼写：iso646.h 头文件"></a>7.3.1 备选拼写：iso646.h 头文件</h3><h3 id="7-3-2-优先级"><a href="#7-3-2-优先级" class="headerlink" title="7.3.2 优先级"></a>7.3.2 优先级</h3><h3 id="7-3-3-求值顺序"><a href="#7-3-3-求值顺序" class="headerlink" title="7.3.3 求值顺序"></a>7.3.3 求值顺序</h3><h3 id="7-3-4-范围"><a href="#7-3-4-范围" class="headerlink" title="7.3.4 范围"></a>7.3.4 范围</h3><h2 id="7-4-一个统计单词的程序"><a href="#7-4-一个统计单词的程序" class="headerlink" title="7.4 一个统计单词的程序"></a><a href="#7.4">7.4 一个统计单词的程序</a></h2><h2 id="7-5-条件运算符："><a href="#7-5-条件运算符：" class="headerlink" title="7.5 条件运算符：?:"></a><a href="#7.5">7.5 条件运算符：?:</a></h2><h2 id="7-6-循环辅助：continue和break"><a href="#7-6-循环辅助：continue和break" class="headerlink" title="7.6 循环辅助：continue和break"></a><a href="#7.7">7.6 循环辅助：continue和break</a></h2><h3 id="7-6-1-continue语句"><a href="#7-6-1-continue语句" class="headerlink" title="7.6.1 continue语句"></a>7.6.1 continue语句</h3><h3 id="7-6-2-break语句"><a href="#7-6-2-break语句" class="headerlink" title="7.6.2 break语句"></a>7.6.2 break语句</h3><h2 id="7-7-多重选择"><a href="#7-7-多重选择" class="headerlink" title="7.7 多重选择"></a><a href="#7.7">7.7 多重选择</a></h2><h3 id="7-7-1-switch语句"><a href="#7-7-1-switch语句" class="headerlink" title="7.7.1 switch语句"></a>7.7.1 switch语句</h3><h3 id="7-7-2-只读每行的首字符"><a href="#7-7-2-只读每行的首字符" class="headerlink" title="7.7.2 只读每行的首字符"></a>7.7.2 只读每行的首字符</h3><h3 id="7-7-3-多重标签"><a href="#7-7-3-多重标签" class="headerlink" title="7.7.3 多重标签"></a>7.7.3 多重标签</h3><h3 id="7-7-2-swtich和if-else"><a href="#7-7-2-swtich和if-else" class="headerlink" title="7.7.2 swtich和if else"></a>7.7.2 swtich和if else</h3><h2 id="7-8-goto语句"><a href="#7-8-goto语句" class="headerlink" title="7.8 goto语句"></a><a href="#7.8">7.8 goto语句</a></h2><h2 id="7-9-关键概念"><a href="#7-9-关键概念" class="headerlink" title="7.9 关键概念"></a><a href="#7.9">7.9 关键概念</a></h2><h2 id="7-10-本章小结"><a href="#7-10-本章小结" class="headerlink" title="7.10 本章小结"></a><a href="#7.10">7.10 本章小结</a></h2><h2 id="7-11-复习题"><a href="#7-11-复习题" class="headerlink" title="7.11 复习题"></a><a href="#7.11">7.11 复习题</a></h2><h2 id="7-12-编程练习"><a href="#7-12-编程练习" class="headerlink" title="7.12 编程练习"></a><a href="#7.12">7.12 编程练习</a></h2><hr>
<p><a name="7.1">7.1 if语句</a></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// colddays.c -- 找出0摄氏度的天数占总天数的百分比</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span> argc, <span class="keyword">char</span> <span class="keyword">const</span> *argv[])</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line">    <span class="keyword">const</span> <span class="keyword">int</span> FREEZING = <span class="number">0</span>;</span><br><span class="line">    <span class="keyword">float</span> temperature = <span class="number">0</span>;</span><br><span class="line">    <span class="keyword">int</span> cold_days = <span class="number">0</span>;</span><br><span class="line">    <span class="keyword">int</span> all_days = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;输入每日的最低温度列表：(q退出)\n&quot;</span>);</span><br><span class="line">    <span class="keyword">while</span> (<span class="built_in">scanf</span>(<span class="string">&quot;%f&quot;</span>, &amp;temperature) == <span class="number">1</span>)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="comment">/* code */</span></span><br><span class="line">        all_days++;</span><br><span class="line">        <span class="keyword">if</span> (temperature &lt; FREEZING)</span><br><span class="line">        &#123;</span><br><span class="line">            cold_days++;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (all_days != <span class="number">0</span>)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;一共 %d 天，其中 %.1f%% 天都是极冷的。\n &quot;</span>, all_days, <span class="number">100.0</span>* (<span class="keyword">float</span>)cold_days / all_days);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (all_days == <span class="number">0</span>)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;没有数据输入！\n&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<p>result：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">输入每日的最低温度列表：(q退出)</span><br><span class="line">12 12 -1 12 12 12 -1 -1 12 12 q</span><br><span class="line">一共 10 天，其中 30.0% 天都是极冷的。</span><br></pre></td></tr></table></figure>

<p>while循环的测试条件是scanf() 的返回值，当读到非数字字符时会返回0，同时将其放入缓冲区，等待下一次读取。temperature 的类型是float 不是 int，这样的程序可以接受像-2.5这样的值，也可以接受8这样的值，会被自动转换为float。<br>使用强制类型转换可以明确表达式转换类型的意图，保护被编译器的影响，虽然可以自动转换，但是还是使用强制转换来提醒。</p>
<p><a name="7.2">7.2 if else语句</a></p>
<ul>
<li><p>getchar() 函数不带任何参数，它从输入队列中返回下一个字符。以下两种写法相同。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">ch =  getchar();</span><br><span class="line"><span class="built_in">scanf</span>(<span class="string">&quot;%c&quot;</span>,&amp;ch);</span><br></pre></td></tr></table></figure>

<p>putchar() 打印字符同理：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">putchar</span>(ch);</span><br><span class="line"><span class="built_in">printf</span>(<span class="string">&quot;%c&quot;</span>,ch);</span><br></pre></td></tr></table></figure>

<p>由于这两个函数只是处理字符，所以比通用的scanf和printf速度更快，更简洁，</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// cypher1.c -- 更改输入，空格不变，非空格替换成ASCII的下一个字符</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> SPACE <span class="meta-string">&#x27; &#x27;</span></span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span> argc, <span class="keyword">char</span> <span class="keyword">const</span> *argv[])</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line">    <span class="keyword">char</span> ch;</span><br><span class="line"></span><br><span class="line">    ch = getchar();</span><br><span class="line">    <span class="keyword">while</span> (ch != <span class="string">&#x27;\n&#x27;</span>)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="comment">/* code */</span></span><br><span class="line">        <span class="keyword">if</span> (ch == SPACE)</span><br><span class="line">        &#123;</span><br><span class="line">            <span class="built_in">putchar</span>(ch);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">else</span></span><br><span class="line">        &#123;</span><br><span class="line">            <span class="built_in">putchar</span>(ch + <span class="number">1</span>);</span><br><span class="line">        &#125;</span><br><span class="line">        ch = getchar();</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="built_in">putchar</span>(<span class="string">&#x27;\n&#x27;</span>);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<p>result：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">aaa bbb ccc</span><br><span class="line">bbb ccc ddd</span><br></pre></td></tr></table></figure>

<p>以上的循环可以替换成：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">while</span>(ch=getchar() != <span class="string">&#x27;\n&#x27;</span>)&#123;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>ctype.h 头文件可以判断字符和数字。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// cypher2.c -- 替换字母，非字母字符不变</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span><span class="meta-string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span><span class="meta-string">&lt;ctype.h&gt;</span></span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span> argc, <span class="keyword">char</span> <span class="keyword">const</span> *argv[])</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line">    <span class="keyword">char</span> ch;</span><br><span class="line">    <span class="keyword">while</span> ((ch = getchar()) != <span class="string">&#x27;\n&#x27;</span>)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="comment">/* code */</span></span><br><span class="line">        <span class="keyword">if</span>(<span class="built_in">isalpha</span>(ch))&#123;</span><br><span class="line">            <span class="built_in">putchar</span>(ch+<span class="number">1</span>);</span><br><span class="line">        &#125;<span class="keyword">else</span></span><br><span class="line">        &#123;</span><br><span class="line">            <span class="built_in">putchar</span>(ch);</span><br><span class="line">        &#125;</span><br><span class="line">        </span><br><span class="line">    &#125;</span><br><span class="line">    <span class="built_in">putchar</span>(ch);</span><br><span class="line">    </span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<p>result：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">Look，it&#39;s a</span><br><span class="line">Mppl，ju&#39;t b</span><br></pre></td></tr></table></figure>

<p>注意判断条件一定是 while ((ch = getchar()) != ‘\n’) 要带括号。因为 != 的优先级高。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// divisors.c -- 使用嵌套if语句显示一个数的约数</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdbool.h&gt;</span></span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span> argc, <span class="keyword">char</span> <span class="keyword">const</span> *argv[])</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line">    <span class="keyword">unsigned</span> <span class="keyword">long</span> num;</span><br><span class="line">    <span class="keyword">unsigned</span> <span class="keyword">long</span> div;</span><br><span class="line">    <span class="keyword">bool</span> isPrime; <span class="comment">// flag 标记 素数标志</span></span><br><span class="line"></span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;输入一个数：q退出\n&quot;</span>);</span><br><span class="line">    <span class="keyword">while</span> (<span class="built_in">scanf</span>(<span class="string">&quot;%lu&quot;</span>, &amp;num) == <span class="number">1</span>)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="comment">/* code */</span></span><br><span class="line">        <span class="keyword">for</span> (div = <span class="number">2</span>, isPrime = <span class="literal">true</span>; (div * div) &lt;= num; div++)</span><br><span class="line">        &#123;</span><br><span class="line">            <span class="keyword">if</span> (num % div == <span class="number">0</span>)</span><br><span class="line">            &#123;</span><br><span class="line">                <span class="keyword">if</span> ((div * div) % num != <span class="number">0</span>)</span><br><span class="line">                &#123; <span class="comment">// 不是完全平方数</span></span><br><span class="line">                    <span class="built_in">printf</span>(<span class="string">&quot;%lu 可以被 %lu 和 %lu 整除\n&quot;</span>, num, div, num / div);</span><br><span class="line">                &#125;</span><br><span class="line">                <span class="keyword">else</span></span><br><span class="line">                &#123;</span><br><span class="line">                    <span class="built_in">printf</span>(<span class="string">&quot;%lu 是完全平方数被 %lu 整除\n&quot;</span>, num, div);</span><br><span class="line">                &#125;</span><br><span class="line">                isPrime = <span class="literal">false</span>;</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">if</span> (isPrime)</span><br><span class="line">        &#123;</span><br><span class="line">            <span class="built_in">printf</span>(<span class="string">&quot;%lu 是素数!\n&quot;</span>, num);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;输入一个数：q退出\n&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;886&quot;</span>);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<p>result：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line">输入一个数：q退出</span><br><span class="line">123456789</span><br><span class="line">123456789 可以被 3 和 41152263 整除</span><br><span class="line">123456789 可以被 9 和 13717421 整除</span><br><span class="line">123456789 可以被 3607 和 34227 整除</span><br><span class="line">123456789 可以被 3803 和 32463 整除</span><br><span class="line">123456789 可以被 10821 和 11409 整除</span><br><span class="line">输入一个数：q退出</span><br><span class="line">149</span><br><span class="line">149 是素数!</span><br><span class="line">输入一个数：q退出</span><br><span class="line">2013</span><br><span class="line">2013 可以被 3 和 671 整除</span><br><span class="line">2013 可以被 11 和 183 整除</span><br><span class="line">2013 可以被 33 和 61 整除</span><br><span class="line">输入一个数：q退出</span><br><span class="line">q</span><br><span class="line">886</span><br></pre></td></tr></table></figure>



</li>
</ul>
<p><a name="7.3">7.3 逻辑运算符</a></p>
<p>&amp;&amp; 与 || 或 ！非 ，引入 iso646.h 头文件可以 and or not 代替</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// chcount.c -- 使用逻辑与运算符</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span><span class="meta-string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdbool.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> PERIOD <span class="meta-string">&#x27;.&#x27;</span></span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span> argc, <span class="keyword">char</span> <span class="keyword">const</span> *argv[])</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line">    <span class="keyword">char</span> ch;</span><br><span class="line">    <span class="keyword">int</span> charcount = <span class="number">0</span>;</span><br><span class="line">    <span class="keyword">while</span> ((ch = getchar() != PERIOD))</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="comment">/* code */</span></span><br><span class="line">        <span class="keyword">if</span>(ch!=<span class="string">&#x27;&quot;&#x27;</span>&amp;&amp;ch!=<span class="string">&#x27;\&#x27;&#x27;</span>)&#123;</span><br><span class="line">            charcount++;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;这里有 %d 个字符.\n&quot;</span>,charcount);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<p>result：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">中文二字符abcd.</span><br><span class="line">这里有 14 个字符.</span><br></pre></td></tr></table></figure>

<p><a name="7.4">7.4 一个统计单词的程序</a></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// wordcnt.c -- 统计字符数，单词数，行数</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdbool.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;ctype.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> STOP <span class="meta-string">&#x27;|&#x27;</span></span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span> argc, <span class="keyword">char</span> <span class="keyword">const</span> *argv[])</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line">    <span class="keyword">char</span> c; <span class="comment">// 读入字符</span></span><br><span class="line">    <span class="keyword">char</span> prev;  <span class="comment">// 读入的前一个字符</span></span><br><span class="line">    <span class="keyword">long</span> n_chars = <span class="number">0L</span>; <span class="comment">// 字符数</span></span><br><span class="line">    <span class="keyword">int</span> n_lines = <span class="number">0</span>; <span class="comment">// 行数</span></span><br><span class="line">    <span class="keyword">int</span> n_words = <span class="number">0</span>; <span class="comment">// 单词数</span></span><br><span class="line">    <span class="keyword">int</span> p_lines = <span class="number">0</span>; <span class="comment">// 不完整的行数</span></span><br><span class="line">    <span class="keyword">bool</span> inword = <span class="literal">false</span>; <span class="comment">// 如果c在单词中，inword为true</span></span><br><span class="line"></span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;输入文本以|结束：\n&quot;</span>);</span><br><span class="line">    prev = <span class="string">&#x27;\n&#x27;</span>;</span><br><span class="line">    <span class="keyword">while</span> ((c = getchar()) != STOP)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="comment">/* code */</span></span><br><span class="line">        n_chars++; <span class="comment">// 统计字符</span></span><br><span class="line">        <span class="keyword">if</span> (c == <span class="string">&#x27;\n&#x27;</span>)</span><br><span class="line">        &#123;</span><br><span class="line">            n_lines++; <span class="comment">// 统计行数</span></span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        <span class="keyword">if</span> (!<span class="built_in">isspace</span>(c) &amp;&amp; !inword) <span class="comment">// 在单词里面</span></span><br><span class="line">        &#123;</span><br><span class="line">            inword = <span class="literal">true</span>;</span><br><span class="line">            n_words++; <span class="comment">// 统计单词</span></span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        <span class="keyword">if</span> (<span class="built_in">isspace</span>(c) &amp;&amp; inword)   <span class="comment">// 一个单词结束</span></span><br><span class="line">        &#123;</span><br><span class="line">            inword = <span class="literal">false</span>; <span class="comment">// 达到单词末尾</span></span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        prev = c;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">if</span>(prev!=<span class="string">&#x27;\n&#x27;</span>)&#123;</span><br><span class="line">        p_lines = <span class="number">1</span>;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;字符数 = %ld,单词数 = %d ,行数 = %d, &quot;</span>,n_chars,n_words,n_lines);</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;不完整的行数为 %d\n&quot;</span>,p_lines);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<p>result:</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line">输入文本以|结束：</span><br><span class="line">Reasin is a</span><br><span class="line">powerful servant but</span><br><span class="line">an inadequate master.</span><br><span class="line">|</span><br><span class="line">字符数 &#x3D; 55,单词数 &#x3D; 9 ,行数 &#x3D; 3, 不完整的行数为 0</span><br><span class="line"></span><br><span class="line">--------------------------------------------------</span><br><span class="line">输入文本以|结束：</span><br><span class="line">123|</span><br><span class="line">字符数 &#x3D; 3,单词数 &#x3D; 1 ,行数 &#x3D; 0, 不完整的行数为 1</span><br></pre></td></tr></table></figure>

<p><a name="7.5">7.5 条件运算符：?:</a></p>
<p>带一个运算对象的称为一元运算符，两个就是二元运算符，3个运算对象的就叫三元运算符。问号语句也叫三元运算符。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// paint.c -- 使用条件运算符</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> COVERAGE 350 <span class="comment">// 每一罐油漆可以刷的面积</span></span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span> argc, <span class="keyword">char</span> <span class="keyword">const</span> *argv[])</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line">    <span class="keyword">int</span> sq_feet;</span><br><span class="line">    <span class="keyword">int</span> cans;</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;输入面积：q退出\n&quot;</span>);</span><br><span class="line">    <span class="keyword">while</span> (<span class="built_in">scanf</span>(<span class="string">&quot;%d&quot;</span>, &amp;sq_feet) == <span class="number">1</span>)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="comment">/* code */</span></span><br><span class="line">        cans = sq_feet / COVERAGE;</span><br><span class="line">        cans += ((sq_feet % COVERAGE == <span class="number">0</span>)) ? <span class="number">0</span> : <span class="number">1</span>;</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;你需要 %d %s 来刷！\n&quot;</span>, cans, cans == <span class="number">1</span> ? <span class="string">&quot;can&quot;</span> : <span class="string">&quot;cans&quot;</span>);</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;输入面积：q退出\n&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<p>result：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">输入面积：q退出</span><br><span class="line">349</span><br><span class="line">你需要 1 can 来刷！</span><br><span class="line">输入面积：q退出</span><br><span class="line">351</span><br><span class="line">你需要 2 cans 来刷！</span><br><span class="line">输入面积：q退出</span><br><span class="line">q</span><br></pre></td></tr></table></figure>

<p><a name="7.6">7.6 循环辅助：continue 和 break</a></p>
<p>continue 跳过当前循环的剩余部分，进入下一次循环；break 终止当前层次的循环。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// skippart.c -- 使用continue跳过部分循环</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span> argc, <span class="keyword">char</span> <span class="keyword">const</span> *argv[])</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line">    <span class="keyword">const</span> <span class="keyword">float</span> MIN = <span class="number">0.0f</span>;</span><br><span class="line">    <span class="keyword">const</span> <span class="keyword">float</span> MAX = <span class="number">100.0f</span>;</span><br><span class="line">    <span class="keyword">float</span> score;</span><br><span class="line">    <span class="keyword">float</span> total = <span class="number">0.0f</span>;</span><br><span class="line">    <span class="keyword">int</span> n = <span class="number">0</span>;</span><br><span class="line">    <span class="keyword">float</span> min = MAX;</span><br><span class="line">    <span class="keyword">float</span> max = MIN;</span><br><span class="line"></span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;输入第一个分数（q退出）:\n&quot;</span>);</span><br><span class="line">    <span class="keyword">while</span> (<span class="built_in">scanf</span>(<span class="string">&quot;%f&quot;</span>, &amp;score) == <span class="number">1</span>)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="comment">/* code */</span></span><br><span class="line">        <span class="keyword">if</span> (score &lt; MIN || score &gt; MAX)</span><br><span class="line">        &#123;</span><br><span class="line">            <span class="built_in">printf</span>(<span class="string">&quot;%0.1f 是一个非法的值，重新输入:&quot;</span>, score);</span><br><span class="line">            <span class="keyword">continue</span>;</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;接收：%0.1f:\n&quot;</span>, score);</span><br><span class="line">        min = (score &lt; min) ? score : min;</span><br><span class="line">        max = (score &gt; max) ? score : max;</span><br><span class="line">        total += score;</span><br><span class="line">        n++;</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;输入第一个分数（q退出）:\n&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">if</span> (n &gt; <span class="number">0</span>)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;一共 %d 个分数的平均分是 %0.1f.\n&quot;</span>, n, total / n);</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;最小值 = %0.1f，最大值 = %0.1f\n&quot;</span>, min, max);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">else</span></span><br><span class="line">    &#123;</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;无效的分数！\n&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<p>result：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line">输入第一个分数（q退出）:</span><br><span class="line">1</span><br><span class="line">接收：1.0:</span><br><span class="line">输入第一个分数（q退出）:</span><br><span class="line">2</span><br><span class="line">接收：2.0:</span><br><span class="line">输入第一个分数（q退出）:</span><br><span class="line">3</span><br><span class="line">接收：3.0:</span><br><span class="line">输入第一个分数（q退出）:</span><br><span class="line">q</span><br><span class="line">一共 3 个分数的平均分是 2.0.</span><br><span class="line">最小值 &#x3D; 1.0，最大值 &#x3D; 3.0</span><br><span class="line"></span><br><span class="line">--------------------------</span><br><span class="line">输入第一个分数（q退出）:</span><br><span class="line">188</span><br><span class="line">188.0 是一个非法的值，重新输入:12</span><br><span class="line">接收：12.0:</span><br><span class="line">输入第一个分数（q退出）:</span><br><span class="line">32</span><br><span class="line">接收：32.0:</span><br><span class="line">输入第一个分数（q退出）:</span><br><span class="line">q</span><br><span class="line">一共 2 个分数的平均分是 22.0.</span><br><span class="line">最小值 &#x3D; 12.0，最大值 &#x3D; 32.0</span><br></pre></td></tr></table></figure>

<p>使用continue为了使代码逻辑简洁，有时也可以增加代码可读性。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">while</span>(getchar()!=<span class="string">&#x27;\n&#x27;</span>)&#123;</span><br><span class="line">	<span class="keyword">continue</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>break 语句对switch语句很重要</p>
<p><a name="7.7">7.7 多重选择：swtich和break</a></p>
<p><img src="https://gitee.com/hardychenlong/giteeblogimg/raw/master/20201022141447.png" class="lazyload" data-srcset="https://gitee.com/hardychenlong/giteeblogimg/raw/master/20201022141447.png" srcset="" alt="image-20201022141440667"></p>
<p><img src="https://gitee.com/hardychenlong/giteeblogimg/raw/master/20201022141531.png" class="lazyload" data-srcset="https://gitee.com/hardychenlong/giteeblogimg/raw/master/20201022141531.png" srcset="" alt="image-20201022141531663"></p>
<p><a name="7.8">7.8 goto语句</a></p>
<p>让它爬。</p>

  
  
    
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        <ol class="toc"><li class="toc-item toc-level-2"><a class="toc-link" href="#7-1-if%E8%AF%AD%E5%8F%A5"><span class="toc-text">7.1 if语句</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#7-2-if-else%E8%AF%AD%E5%8F%A5"><span class="toc-text">7.2 if else语句</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#7-2-1-%E4%BB%8B%E7%BB%8Dgetchar"><span class="toc-text">7.2.1 介绍getchar()</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#7-2-2-ctype-h-%E7%B3%BB%E5%88%97%E7%9A%84%E5%AD%97%E7%AC%A6%E5%87%BD%E6%95%B0"><span class="toc-text">7.2.2 ctype.h 系列的字符函数</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#7-2-3-%E5%A4%9A%E9%87%8D%E9%80%89%E6%8B%A9else-if"><span class="toc-text">7.2.3 多重选择else if</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#7-2-4-else%E4%B8%8Eif%E9%85%8D%E5%AF%B9"><span class="toc-text">7.2.4  else与if配对</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#7-2-5-%E5%A4%9A%E5%B1%82%E5%B5%8C%E5%A5%97%E7%9A%84if%E8%AF%AD%E5%8F%A5"><span class="toc-text">7.2.5 多层嵌套的if语句</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#7-3-%E9%80%BB%E8%BE%91%E8%BF%90%E7%AE%97%E7%AC%A6"><span class="toc-text">7.3 逻辑运算符</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#7-3-1-%E5%A4%87%E9%80%89%E6%8B%BC%E5%86%99%EF%BC%9Aiso646-h-%E5%A4%B4%E6%96%87%E4%BB%B6"><span class="toc-text">7.3.1 备选拼写：iso646.h 头文件</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#7-3-2-%E4%BC%98%E5%85%88%E7%BA%A7"><span class="toc-text">7.3.2 优先级</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#7-3-3-%E6%B1%82%E5%80%BC%E9%A1%BA%E5%BA%8F"><span class="toc-text">7.3.3 求值顺序</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#7-3-4-%E8%8C%83%E5%9B%B4"><span class="toc-text">7.3.4 范围</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#7-4-%E4%B8%80%E4%B8%AA%E7%BB%9F%E8%AE%A1%E5%8D%95%E8%AF%8D%E7%9A%84%E7%A8%8B%E5%BA%8F"><span class="toc-text">7.4 一个统计单词的程序</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#7-5-%E6%9D%A1%E4%BB%B6%E8%BF%90%E7%AE%97%E7%AC%A6%EF%BC%9A"><span class="toc-text">7.5 条件运算符：?:</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#7-6-%E5%BE%AA%E7%8E%AF%E8%BE%85%E5%8A%A9%EF%BC%9Acontinue%E5%92%8Cbreak"><span class="toc-text">7.6 循环辅助：continue和break</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#7-6-1-continue%E8%AF%AD%E5%8F%A5"><span class="toc-text">7.6.1 continue语句</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#7-6-2-break%E8%AF%AD%E5%8F%A5"><span class="toc-text">7.6.2 break语句</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#7-7-%E5%A4%9A%E9%87%8D%E9%80%89%E6%8B%A9"><span class="toc-text">7.7 多重选择</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#7-7-1-switch%E8%AF%AD%E5%8F%A5"><span class="toc-text">7.7.1 switch语句</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#7-7-2-%E5%8F%AA%E8%AF%BB%E6%AF%8F%E8%A1%8C%E7%9A%84%E9%A6%96%E5%AD%97%E7%AC%A6"><span class="toc-text">7.7.2 只读每行的首字符</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#7-7-3-%E5%A4%9A%E9%87%8D%E6%A0%87%E7%AD%BE"><span class="toc-text">7.7.3 多重标签</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#7-7-2-swtich%E5%92%8Cif-else"><span class="toc-text">7.7.2 swtich和if else</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#7-8-goto%E8%AF%AD%E5%8F%A5"><span class="toc-text">7.8 goto语句</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#7-9-%E5%85%B3%E9%94%AE%E6%A6%82%E5%BF%B5"><span class="toc-text">7.9 关键概念</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#7-10-%E6%9C%AC%E7%AB%A0%E5%B0%8F%E7%BB%93"><span class="toc-text">7.10 本章小结</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#7-11-%E5%A4%8D%E4%B9%A0%E9%A2%98"><span class="toc-text">7.11 复习题</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#7-12-%E7%BC%96%E7%A8%8B%E7%BB%83%E4%B9%A0"><span class="toc-text">7.12 编程练习</span></a></li></ol>
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        elements: 'a[href]:not([href^="#"]):not([href="javascript:void(0)"]):not([pjax-fancybox])',
        selectors: [
          "title",
          "#pjax-container",
          "#pjax-header-nav-list"
        ],
        cacheBust: false,   // url 地址追加时间戳，用以避免浏览器缓存
        timeout: 5000
      });
    });

    document.addEventListener('pjax:send', function (e) {
      window.stop(); // 相当于点击了浏览器的停止按钮

      try {
        var currentUrl = window.location.pathname;
        var targetUrl = e.triggerElement.href;
        var banUrl = [""];
        if (banUrl[0] != "") {
          banUrl.forEach(item => {
            if(currentUrl.indexOf(item) != -1 || targetUrl.indexOf(item) != -1) {
              window.location.href = targetUrl;
            }
          });
        }
      } catch (error) {}

      window.subData = null; // 移除标题（用于一二级导航栏切换处）
      if (typeof $.fancybox != "undefined") {
        $.fancybox.close();    // 关闭弹窗
      }
      $('.l_header .switcher .s-search').removeClass('active'); // 关闭移动端激活的搜索框
      $('.l_header').removeClass('z_search-open'); // 关闭移动端激活的搜索框
      $('.wrapper').removeClass('sub'); // 跳转页面时关闭二级导航

      // 解绑事件 避免重复监听
      $('.s-top').unbind('click');
      $('.menu a').unbind('click');
      $(window).unbind('resize');
      $(window).unbind('scroll');
      $(document).unbind('scroll');
      $(document).unbind('click');
      $('body').unbind('click');
      window.ShowLoading();
    });

    document.addEventListener('pjax:complete', function () {
      // 关于百度统计对 SPA 页面的处理：
      // 方案一：百度统计>管理>单页应用设置中，打开开启按钮即可对SPA进行统计。 https://tongji.baidu.com/web/help/article?id=324
      // 方案二：取消注释下列代码。 https://tongji.baidu.com/web/help/article?id=235
      // 

      // 关于谷歌统计对 SPA 页面的处理：
      // 当应用以动态方式加载内容并更新地址栏中的网址时，也应该更新通过 gtag.js 存储的网页网址。
      // https://developers.google.cn/analytics/devguides/collection/gtagjs/single-page-applications?hl=zh-cn
      

      $('.nav-main').find('.list-v').not('.menu-phone').removeAttr("style",""); // 移除小尾巴的移除
      $('.menu-phone.list-v').removeAttr("style",""); // 移除小尾巴的移除
      $('script[data-pjax], .pjax-reload script').each(function () {
        $(this).parent().append($(this).remove());
      });
      try{
          if (typeof $.fancybox == "undefined") {
            SCload_fancybox();
          } else {
            pjax_fancybox();
          }
        
          
          if ('.cover-backstretch') {
            $('.cover-backstretch').backstretch("resize");
            if($('.cover-wrapper').is(':hidden')){
              $('.cover-backstretch').backstretch("pause");
            }else{
              $('.cover-backstretch').backstretch("next");
            }
          } else {
            $.backstretch("resize");
            if($('.cover-wrapper').is(':hidden')){
              $.backstretch("pause");
            }else{
              $.backstretch("next");
            }
          }
        
        
        document.querySelectorAll('pre code').forEach((block) => {
          hljs.highlightBlock(block);
        });
        
        
          pjax_scrollrebeal();
        
        
        
          pjax_initCopyCode();
        
        
          pjax_valine();
        
        
        
        
        
          pjax_darkmodejs();
        
      } catch (e) {
        console.log(e);
      }
      window.HideLoading();
    });

    document.addEventListener('pjax:error', function (e) {
      window.HideLoading();
      window.location.href = e.triggerElement.href;
    });
</script>

    
  </div>
</body>
</html>
